Bioluminescent fish — marine species capable of producing their own light — have evolved on a much wider scale than previously thought, according to a recent report published in the journal PLOS ONE.
Bioluminescence is a unique trait generally thought to be enjoyed by only a few species. In the dark depths of the ocean, it is used a means of communication, to deter predators, or locate prey.
The first ocean fish to have this ability appeared during the Cretaceous period roughly 150 million years ago. Since then, researchers who analyzed a wide range of bioluminescent fish in order to trace their origins say the trait spread to many different species.
They found that the trait was present 29 times in marine fish across 14 different clades — groups that come from a single ancestor — with likely even more such species out there, Live Science reports.
Prior to this new study, scientists believed that bioluminescence evolved just 40 times across all known animal species. Finding 29 instances just in fish alone drastically changes that perception.
“When things evolve independently multiples times, we can infer that the feature is useful,” said co-author W. Leo Smith, from the University of Kansas, in a statement. “You have this whole habitat where everything that’s not living at the top or bottom of the ocean or along the edges — nearly every vertebrate living in the open water — around 80 percent of those fish species are bioluminescent. So this tells us bioluminescence is almost a requirement for fishes to be successful.”
The team also found that once bioluminescence appeared within a lineage, that lineage quickly diversified. Those that used light to communicate were particularly varied.
Fish create light for numerous reasons. For instance, the dragonfish uses light-producing organs on their stomachs — known as photophores — to blend in with the meager light coming down from the surface. This helps them hide from potential predators that may be looking at them from below.
Another type of photophore located on a fish’s face is often used for communication and some species have flexible, light-up appendages that attract prey. The arrangement of communication light organs varies from species to species.
The team plans to continue their research by studying bioluminescence on a genetic level. They hope this will help them understand the way the trait evolved and how fish came to catalyze the chemical that allows them to glow.
But, for now, many questions still remain.
“Many fishes proliferate species when they evolve this trait — they differentiate, but we don’t know why,” added Smith. “In the ocean, there are no physical barriers to separate groups of deep-sea fishes, so why are there so many species of anglerfishes, for example? When they start using bioluminescence for species recognition, they diversify into a lot more species.”